1. Field of the Invention
The present invention relates to a projector device adapted to guide light from a light source to an optical system to generate image light for magnification projection on a forward screen.
2. Description of Related Art
A conventional projector device of this type includes a casing having disposed therein a lamp for serving as a light source, and an optical system including a polarization beam splitter, a polarizing plate, liquid crystal panels, a projection lens, etc. (see JP 10-274752, A). The polarization beam splitter has a function of extracting only one component wave out of P- and S-waves of light, which allows a liquid crystal panel to be irradiated with light polarized in the same direction.
FIG. 6 shows a polarization beam splitter 25 in a liquid crystal projector device of the present invention. Because the polarization beam splitter 25 has the same configuration also in the conventional liquid crystal projector, a conventional polarization beam splitter 25 will be described below with reference to the same drawing. As shown in FIG. 6, the polarization beam splitter 25 includes a polarizing plate 25a and a half-wavelength plate 25b with slits joined to a light emergence surface thereof. Inside the polarizing plate 25a, first interfaces 125 for passing therethrough a P-wave of light incident on the polarizing plate 25a and reflecting an S-wave, and second interfaces 126 for reflecting the S-wave are alternately formed with an inclination angle of 45 degrees relative to the surface of the polarizing plate 25a. 
The P-wave of the light incident on the first interfaces 125 passes through the first interfaces 125 to reach the half-wavelength plate 25b. The P-wave has a phase thereof inversed by passing through the half-wavelength plate 25b, and emerges as an S-wave. On the other hand, the S-wave reflected by the first interfaces 125 reaches the second interfaces 126, and is reflected by the second interfaces 126 to emerge from each slit 25c of the half-wavelength plate 25b. Thus, only the S-waves emerge from the polarization beam splitter 25.
An aluminum slit plate 24 is placed at a light incidence side of the polarizing plate 25a because the polarization function of the polarization beam splitter 25 degrades if light is incident on the second interfaces 126 in the polarization beam splitter 25. Each slit 24a of the slit plate 24 is provided in a position that allows light incidence on the first interfaces 125, but light incidence on the second interfaces 126 is prevented by the slit plate 24. The slit plate 24 is placed in contact with a light incidence surface of the polarization beam splitter 25, or in a position close to the surface, in order to maintain relative position accuracy between the first interfaces 125 of the polarization beam splitter 25 and a plurality of slits 24a provided in the slit plate 24.
The polarization beam splitter 25 significantly degrades the polarization function upon exceeding a limit temperature, and therefore needs to be used in a range within the limit temperature. However, heat is transmitted to the polarization beam splitter 25 from the slit plate 24, which could have a high temperature upon receipt of the light from the light source, because the slit plate 24 is placed in contact with the surface of the polarization beam splitter 25, or in a position close to the surface. This has caused a problem of the polarization beam splitter 25 having a high temperature exceeding a limit temperature.